With increasing energy cost, considerable attention has been directed to developing alternative forms of energy, i.e. forms of energy which will permit the heating of a building, using other than conventional fuels and electrical energy.
For example, it is known that a considerable amount of heat is lost through the walls of a building which, even if insulated, constitute a significant radiator of thermal energy, especially when the temperature differential across the wall is considerable. In temperate and like weather zones, the temperature differential across the walls of a heated structure, especially in the wintertime, can be tens of degrees celsius thereby driving thermal energy from the interior outwardly and causing a significant loss of heat unless this so-called lost energy can be recovered.
It is also known that a considerable amount of thermal energy is available from solar energy impinging upon the large surface areas of building structures. Finally, in many cases the ambient atmosphere contains recoverable thermal energy. Such thermal energy may be in the form of warm air adjacent the building.
Various techniques have been proposed to recover and/or utilize and/or conserve these quantities of thermal energy. Thus, for example, the walls of the building structure may be highly insulated to prevent loss of heat to the external environment. Solar energy systems may be provided, e.g. on roof structures, to convert the impinging solar energy radiation into a heated fluid or the like whose sensible heat can be effectively utilized.
However, in practice it has not been found to be advantageous, convenient or desirable to utilize the thermal energy of the air and even the utilization of solar energy has been minimal because of the considerable costs of so-called solar energy converters as have been proposed heretofore.
In German published application (Offenlegungsschrift) DT-OS No. 2,511,861, for example, there has been described an apparatus permitting the utilization of solar energy in combination with a building structure. In this system, an air inlet is provided and a blower or the like draws ambient air through a first heat exchanger which is exposed to the solar energy so that the warm air can be fed to a second heat exchanger forming part of the heat-utilization system.
While this arrangement effectively permits some utilization of solar energy, it is relatively inefficient and has not proved to be fully satisfactory.